High capacity single tank water clarification system

ABSTRACT

Raw feed water is continuously clarified at a large throughput rate in a single, shallow tank using a flotation process carried out simultaneously in multiple sectors of the tank. Raw water feeds into a rotating trough. A fixed manifold system in the trough dispenses pressurized water containing dissolved air to release microscopic air bubbles. A set of headers each radially extend outwardly from the rotating trough. Each header distributes water and bubbles to a sector of the tank with a net zero velocity. A set of rotating extractors each receive clarified water from the bottom of a preceding sector. A set of scoops skim floated sludge from the water in the tank. The sludge is lifted, as by the rotation of the scoop and/or by a pumped conduit, over the rotating trough to a sludge outlet pipe. In one form the scoop has at least two blades each with an eccentrically located, radially extending compartment that receives, lifts, and then dumps the skimmed sludge as the scoop rotates about its axis.

BACKGROUND OF THE INVENTION

This invention relates in general to apparatus and a process for theflotation clarification of water. More specifically, it relates to anapparatus and process where multiple such processes are carried outsimultaneously in a single tank to provide an extremely high treatmentrate with a high degree of compactness.

Water clarification, the removal of particulate contaminants suspendedin water, is used to treat waste water from manufacturing processes,particularly in the pulp and paper industries, in the treatment ofmunicipal water drinking supplies, and in sewage treatment. The watercan be clarified by sedimentation or flotation of the particles. Knownsedimentation techniques and apparatus are efficient, but even at peakefficiency they are limited to a comparatively slow sedimentation rate,about 0.5 gallons per minute per square foot. To handle large volumes ofraw input water, sedimentation facilities must therefore be large, withattendant cost and space utilization disadvantages.

Flotation techniques dissolve a few percent of air by volume inpressurized water and then release the air in the form of microscopicbubbles which attach to the particles and carry them to the surfacewhere they form a floating sludge. The particles are usually flocculatedusing conventional flocculating agents such as alum. Flotationtechniques are theoretically capable of achieving clarification rates of7.5 gallons per minute per square foot of flotation area.

Applicant holds several U.S. patent on apparatus and processes for waterclarification by flotation. U.S. Pat. Nos. 2,874,842 and 3,182,799introduce gas bubbles to a tank with no moving components inside or overthe tank. Internal deflectors and baffles guided the water and theflotation process; the turbulence of the water was minimal and did notpresent a design problem. This equipment, however, operated slowly.

U.S. Pat. No. 4,022,696 describes an improved clarifier of applicantsold commercially under the trade designations "SPC", "Supracell", and"Supercell". Flotation occurs in a circular tank. Raw water is fed froma raw water inlet pipe at the center of the tank, a hydraulic joint, anda manifold that rotates about the tank. The inlet flow from the manifoldis directed opposite to the direction of rotating so that the raw waterentering the tank has a net zero velocity. Flocculation occurs in aflocculation chamber, an assembly of pipes, walls and baffles that isimmersed in the tank and rotates on a carriage with the manifold.Another rotating manifold introduces dissolved air to the flotation tankfollowing the flocculation assembly. A rotating scoop, preferably amultiple blade scoop of the type described in applicant's U.S. Pat. No.4,184,567 is also carried on the carriage. It scoops the floated sludgefrom the surface of the tank and directs it to a central pipe that isinclined to gravity feed the collected sludge to a central collectioncompartment.

The carriage rotates about the tank at a rate such that the floatedparticles reach the surface in about one rotation. With a flotation rateof 12 inches per minute, a good degree of clarification can be achievedwith each rotation using a comparatively shallow tank, e.g. 16 to 18inches of water. While these units, operated in this manner, are muchmore efficient than the earlier stationary equipment, and in generalthey are highly successful, they do not provide a throughput capacitythat can handle a large municipal treatment plant without utilizing alarge number of the apparatus. For example, to treat raw water input at8 to 9 m³ /sec would require more than twelve SPC units of the largestsize, a 70 foot (about 22m) diameter which processes 11,800 gallons perminute, or 0.73 m³ /sec. This many units has serious disadvantages interms of capital cost, operating cost, and space utilization. Further,simply increasing the size of each unit and operating it at a fasterspeed does not provide an acceptable solution since the increased speedof rotation of the carriage required to take advantage of the increasedsize creates turbulence as the flocculation assembly and dissolved airmanifold move through the water with an increased velocity. Also, a netzero velocity operation is more difficult to achieve at higherrotational speeds.

U.S. Pat. No. 4,377,485 discloses a clarifier (sold under the tradedesignation "SAF") operating with the same features as the SCP unit, butadding a second filtration stage, a set of sand beds covering the bottomof the tank. While the clarified water is cleaner than with a comparableSPC unit, the SAF has a higher initial cost and does not increase thefiltration rate.

U.S. Pat. No. 4,626,345 discloses a further clarifier sold under thetrade designation "SASF". This unit does not employ the SPC's zerovelocity principle, but it does offer two stage filtration with sand ata favorable cost and compactness as compared to the SAF unit. Raw waterin this unit enters a central cylindrical compartment at the bottom.This compartment acts as a hydraulic flocculator. Aerated water isintroduced to this central compartment by a fixed manifold located nearthe upper end of the compartment. Flocculated and aerated water is fedto a clarification tank by flowing over the upper edge of thecylindrical compartment into the surrounding tank. This unit providesgood clarification with a compact unit, but it does not offer thethroughput capacity or overall performance of the SPC or SAF units.

U.S. Pat. No. 4,931,175 discloses another SPC-type clarifier where a setof concentric, conical plates rotate within the tank to increase thelength of the path traversed by the rising bubbles. With thisarrangement, it is possible to increase the treatment capacity of agiven diameter tank, with the increase being roughly approximated by thedegree to which adjacent ones of these conical plates overlap oneanother. A 50% increase in the flotation rate, for example, is wellwithin theoretically possible limits. However, in practice it has beenfound that it is difficult to obtain consistent increases that equal thetheoretical maximum. Moreover, even if the inclined plates worked aswell as theoretically possible, they would not increase the treatmentcapacity of an SPC unit sufficiently to treat raw water at throughputrates as high as 8-9 m³ /sec, values necessary in certain applicationssuch as the treatment of the municipal waste of a major city byretrofitting existing sedimentation tanks with a fixed area.

It is therefore a principal object of this invention to provide aflotation-type water clarification apparatus and process which has agreatly increased filtration rate for a given diameter tank.

Another principal object is to provide a clarifying system with thisgreatly increased rate in a compact size that does not requiresignificant additional space, e.g. room for multiple known SPC-typeclarifiers.

A further object is to provide a clarifying system with the foregoingadvantages that has a comparatively low capital cost and weight ascompared to a comparably sized SPC or SAF unit.

Another object is to provide a clarifying system with the foregoingadvantages that can retrofit existing sedimentation units.

Yet another object is provide a scoop that removes floated sludge at ahigh rate and lifts it to promote its movement to a collectioncompartment.

A still further object is to provide a flotation clarifier with all ofthe foregoing advantages that has a simplified water distribution andlevel control that avoids rotary seals, particularly at a raw waterinlet feeding flotation tank.

SUMMARY OF THE INVENTION

A clarifier of raw water carrying suspended particulate contaminants isorganized about a generally cylindrical, shallow tank that is open atits center to accommodate an inlet pipe for the raw water, whichpreferably has been treated with a flocculating agent, and a sludgeremoval pipe. The sludge removal pipe is preferably capped by a conicalfunnel that directs sludge collected from the surface of the tank by aset of scoops to the pipe. The funnel preferably overlies an upward flowof raw water from the inlet and then downward to a fixed trough thatsurrounds the inlet. The raw water overflows the outer cylindrical wallof the fixed trough to a surrounding, rotating trough having a bottomwall and inner and outer cylindrical walls. The inner wall is preferablyin a sliding seal with the outer wall of the fixed trough, being engagedat its upper end in a downwardly facing flange fixed on the outer wallof the fixed trough. A supply of pressurized water contained dissolvedair is directed by distribution ring set in the fixed trough, feedconduits bridging to the rotating trough, and a set of manifolds with aplurality of narrow-gap outlets to the rotating trough. A supply oftreated raw water containing microscopic air bubbles for flotationclarification is thus created in a compact area, without the use of arotary seal or sophisticated water level controls.

The rotating trough feeds water and bubbles to the tank via a set ofheaders that extend radially from the trough into the tank. The headersare preferably box-like, relatively flat, wide in the direction ofrotation, and occupy an upper portion of the tank. This configurationpermits a small profile in the direction of rotation to reduceturbulence created by movement of the headers in the water. Thecircumferential "width" provide an unrestricted flow path from thetrough into the header and acts as a small, local supply of aerated rawwater within the tank. This reduces the turbulence of the water as itenters the tank. The box preferably has a cross sectional area thatincreases slightly with the radius to present a generally uniformpressure profile as a function of radius. Multiple outlets feed thewater from the header to the tank. The outlets are spaced and sized tofeed a roughly equal volume of raw water to the tank at any givenradius. Significantly, they are also directed generally opposite to thedirection of rotation so that the water entering the tank has a net zerovelocity. The headers are preferably equiangularly spaced with respectto one another.

A spider-like carriage rotates around the tank. It supports the headersand a like array of radially extending extractors. Each extractorreceives clarified water from the bottom of the tank via a set of inletspreferably arrayed along the front or bottom surfaces of a box-likestructure similar to the headers. Each extractor is associated with aheader and preferably positioned ahead of the headers to withdraw waterthat has been clarified in the sector of the tank between that extractorand the immediately preceding header. The headers and extractors formsets of rotating radially directed lines of water distribution andextraction.

Clarified water proceeds through each header to an annular collectionchamber located below the rotating trough, and defined in part by theouter wall of the trough and its bottom wall. In the preferred form asliding contact seal such as a rubber skirt secured on the outer wall ofthe tank forms the seal. The collection compartment empties directly toa clarified water outlet pipe. Also in the preferred form, the extractorhas a sediment rake secured to it that scrapes large particles thatsettle in the tank to one or more sediment collection sumps that feedoutlet pipes.

The floated, flocculated contaminants collect on the surface of thewater held in the tank as a floating layer of sludge. There ispreferably a scoop mounted on the carriage with each header--extractorpair. The scoop has at least one and preferably two blades that extendradially over the tank. The scoop rotates about its own axis as well asbeing rotated about the center of the tank on the carriage. In eachrevolution of the scoop it skims sludge from the tank, lifts it abovethe surface of the water, and then dumps it onto an inclined slide thatguides the sludge to the funnel and the sludge removal pipe. To lift thesludge, each blade directs skimmed sludge to an associated compartmentwhich is radially offset from the axis of rotation of the scoop. Thecompartment is configured to dump the sludge during a position of eachrotation, when the sludge is carried by the rotation to a point raisedover the surface of the water. In another form, the sludge is directedto a known passageway at the center of the scoop which is in turninclined to feed the sludge toward the center of the tank. There aconduit and a pump lift the sludge to an inclined trough that bridgesthe rotating trough and directs the sludge to the funnel.

Broadly stated, the process of the present invention involves operatingmultiple clarification sectors simultaneously in a single tank. Toimplement this process, the invention involves distributing raw water tothe tank along angularly spaced, radially directed lines, removingclarified water from the tank along n angularly spaced, radiallydirected lines, rotating these lines in unison to define rotatingsectors of clarification within the tank each defined by one of thelines of distribution and a following line of removing, and clarifyingthe water in each of said sectors by flotation. The process furtherincludes removing floated sludge from the surface of the tank,preferably along plural rotating, radially directed lines. Thedistributing of the water to the tank is with a net zero velocity. Theprocess further includes releasing microscopic air bubbles into the rawwater at the center of the tank and distributing this water and bubblesto the rotating lines.

These and other features and objects will be more fully understood fromthe following detailed description which should be read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a high capacity, single tank waterclarification system according to the present invention;

FIG. 2 is a view in vertical section taken along the line 2--2 in FIG.1;

FIG. 3 is a detailed view of the rotating water aeration anddistribution tank shown in FIGS. 1 and 2; and

FIG. 4 is a simplified end view of one form of rotating scoop thatcollects floated sludge and lifts it.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-4 show a high capacity, single tank water clarifier 10 accordingto the present invention. It operates on the flotation principal totreat raw water containing suspended solid contaminants. Raw water isfed by an inlet or supply line 12 to a generally circular tank 14 wherethe clarification occurs. Clarified water flows out of the clarifier viaan outlet conduit 16. A feed line 18 adds a flocculating agent such asalum to the raw water supply line 12. Pressurized water with one to twopercent dissolved air is introduced via a supply ring 20, bridgingdistribution arms 22, and outlet manifolds 24. Each manifold 24 has aset of outlets 24a with a narrow exit orifice. As is well known in theart, the pressure drop experienced by the water exiting through thisnarrow orifice releases the dissolved air in the form of a high densityof microscopic bubbles. The unit 10 includes a spider-like carriage 26that supports and rotates a set of headers 28, extractors 30 and sludgeremoval scoops 32 arrayed in three radially extending arms 26a, 26a,26a.

As shown, the tank 14 is set in a pre-existing, circular sedimentationtank 34. To retrofit the tank 34, back fill 36 with an overlying layer38 of poured concrete fills the tank 34 yielding a flat bottom thatsupports a bottom wall 14a of the flotation tank 14. The tank 14 isshallow. A typical depth for the water w held in the tank 14 is sixteento eighteen inches. The tank as shown has a diameter of forty fivemeters, although it will be understood that the diameter and depth canvary. If the tank 14 is not so retrofit, its generally flat bottom wall14a can be supported on steel I beams or any of a wide variety ofstructures. Because the water in the tank is shallow, it does not havethe large mass of a comparably sized sedimentation tank filled withwater to a much greater depth. An outer wall 14b is generally circular.Several sumps 40 formed in the bottom wall 14a collects largeparticulate matter that settles in the tank 14 despite the flotationprocess. A sedimentation rake 42 sweeps the sedimentation along thebottom wall to the sumps. Conduits 44, 44 carry the sediment from theclairifier 10.

The raw water supply line 12 is centered within the tank 14. An upwardlydirectly flow spills over into a fixed trough 48 defined by theinnermost portion of the bottom wall 14a and a circular outer wall 48a.As shown the trough 48 has a diameter of about 15m and the outer wallhas a height of 0.8m. The dissolved air ring 20 is located in thetrough. It is fed by a conduit 20a extending through the bottom wall ofthe trough. The arms 22 bridge the outer wall to carry pressurized andaerated water to manifolds 24. Their outlets 24a are immersed in waterheld in a rotating trough 50 that surrounds the fixed trough 48concentrically. In the first tank the turbulence of the raw water isdissipated and the alum is mixed with the raw water. The height of theouter wall 48a sets the water level, and to some degree controls theflow of the raw, alum-treated water, because raw water is fed outwardlyto the trough 50 by overflowing the wall 48a.

The rotating trough 50 has a bottom wall 50a, an outer wall 50b and aninner wall 50c. The outer wall has a resilient skirt 52 that is in asliding contact seal with the bottom wall 14a of the tank that blocks aninward flow of water from the tank. The wall 50b extends above theheight of the wall 48a to block a direct outward flow of the water fromthe trough 50 to the tank by simply overflowing this wall. As best seenin FIG. 3, the outer wall 48 has a downwardly open recess 48a at itsouter surface that receives the upper edge of he rotating inner wall50c. This arrangement provides a sliding seal that blocks water oneither side of the wall 50c from flowing back into the trough 48. Also,a circular weir 54 confines the turbulent spilled over water in a region50d of the trough. The water moves to the main region 50e of the trough50 by flowing over the top edge of the weir. The raw water held in thetrough region 50e is then chemically treated, aerated with microscopicair bubbles, isolated from the turbulence of the infeed, and has itslevel automatically controlled by the walls 48a and 50b.

A set of the hollow, box-like headers 28 constitute another principalfeature of this invention. They each extend radially across the tank 14from the wall 50b down to the wall 14b. Each header has upper and lowerwalls 28a, 28b, front and rear walls 28c, 28d and an end wall 28e. Atthis inner end, each header is in fluid communication with the troughregion 50e through an aligned opening 50f in the outer wall 50b. Thewalls 28a-28d are preferably mounted on and sealed to the wall 50b. Aset of outlets 56 set in the rear wall 28d direct the treated waterflowing radially within the header and exit to the tank via the outlets56. The outlets are oriented so that the flow to the tank is in adirection generally opposite to that of the header itself as indicatedby arrow 58. The size and orientation of the outlets is selected inconjunction with the rate of rotation of the header to produce a netzero velocity of the treated water as it enters the tank. This avoidsturbulence and is conducive to producing a generally vertical path offlotation for the bubbles and the particulate contaminants adhering tothe bubbles. Both of these conditions are in turn conducive to a rapidclarification of the water in a shallow depth.

The headers are flat, wide circumferentially, and have an internal crosssectional area that increases slightly as a function of radius tofacilitate a uniform pressure drop along the header. This uniformity, inconjunction with a mutual spacing of the outlets that decreases as afunction of the radius along the header promotes a distribution oftreated water inlet flow to the tank that is generally uniform radiallyacross the tank. The flow is uniform as a function of the volume of rawwater input to a unit vollame of the tank swept out by the header as itrotates. The end result is that each unit volume of the tank receivesabout the same volume of treated water regardless of the location of theunit volume within the tank. The flatness of the tank helps to reduceturbulence due to movement of the header within the tank. The widthallows a uniform, laminar flow of the treated water radially within theheader. The flatness--a typical value being 50 cm--also allows theheaders to rotate in an upper half of the tank while the extractorsrotate in a lower half.

The extractors 30 are of generally the same construction as the headersexcept that they have inlets 60 located on their front wall 30c, andhave no outlets or inlets on their rear wall 30d. The inlets arelocated, spaced, sized and oriented to receive clarified water from aregion near the bottom wall of the tank. The extractor directs theinflowing water radially, along the hollow interior of the extractor, toan opening 50g in the trough wall 50b that communicates only with anassociated one of the extractors. Water flowing through each opening 50genters an annular clarified water collection compartment 62 defined bythe lower portion of the wall 14a, the outer wall 48a, the recess 48b,the inner wall 50c received in the recess, and the rotating troughbottom wall 50a. The compartment 62 collects water from all theextractors and feeds it to the outlet 16, which passes through the layer38, backfill 36 and sedimentation tank 34.

The extractors extend radially across the tank and lie in a lower halfof the tank. Their flat profile also aids in reducing turbulence due tothe movement through the water. Each extractor removes clarified waterfrom sector 64 of the tank 14 defined between that extractor and therotationally preceding header. To make maximum use of the tanks, eachextractor precedes only slightly the distributor supply treated rawwater to the following sector 64. This close grouping of extractors andheaders facilitates supporting and rotating them in unison on thecarriage 26. The comparatively large and radially increasingcircumferential width of each extractor accommodate the rapid influx ofclarified water from entire tank, and especially the relatively largerinflux from the outer regions where there is a greater volume of waterswept out by the rotating extractor in a given interval than closer tothe wall 50b.

The carriage 26 has a central support post 26a, a central bearing 26b, acircular mounting platform 26c mounted on the bearing for free rotationabout the post 26a, a rotary electrical joint 26d that connectselectrical power to the carriage, and a pair of generally radiallydirected support arms 26e, 26f associated with each header-extractorpair. Motors 66 drive wheels 68 propel the carriage 26 and the headers28, extractors 30, scoops 32 and trough 50 mounted on the carriage torotate in unison. Idler wheels 70, typically six, roll on the bottomwall 14a and support each header-extractor-scoop set. Cables 71 extendbetween the ends of adjacent arms of the carriage to ensure that thecarriage moves in unison with a uniform angular spacing between itsarms.

The carriage 26 also supports the scoops 32 and rotates them around thetank over the surface of the water w held in the tank. A motor 72 andchain or belt drive 74 located on each assembly 26g rotate the scoopabout its own longitudinal axis, as indicated by arrow 76 in FIG. 4. Thescoop can be one of a known, multi-blade type described in U.S. Pat. No.4,184,567. In this scoop, multiple curved blades skim floated sludgesfrom the surface of the tank. Continued rotation directs the scoopedsludge to a central passageway that is inclined to gravity feed thesludge to a central collection point. In the preferred form shown inFIG. 4, each scoop has two diametrically opposed blades 32a that have agenerally truncated conical configuration that rotate about a commonaxis of rotation 32b. Interior walls 32c lying along a "chord" form acompartment 32d that holds the sludge until the sludge scooped at the 6o'clock position as shown is raised to a dumping position, at about oneto three o'clock as shown. A radially extending sludge trough 78receives the dumped sludge. The trough 78 is inclined to gravity feedthe sludge toward an end adjacent the wall 50b. A fixed blade 79 guidesthe dumped sludge from the compartments to the trough 78. The scoopitself is also inclined in the same direction, as best seen in FIG. 2.The lifting action of the compartments 32d thus allows the inclinationof the scoop to be added to that of the trough 78 to obtain a bettergravity feed than with either acting alone.

The scoop 32 also has a set of diametrically opposed blades 32e, 32ethat also have a truncated conical configuration with one edge joinedwith an end of one of the walls 32c. Sludge enters the scoop at theopenings 32f, 32f. Continued rotation carries the sludge onto interiorwalls 32g, 32g. Still further rotation dumps the sludge into the trough78, again at the one to three o'clock positions. Rotation of this scoop32, having a diameter at its outer end of 80 to 100 cm and diameter atits inner end of 40 to 50 cm and rotated at about 1 revolution perminute has been found about to remove the accumulated floating sludgefrom surface of the tank at a rate that can keep up with the high volumeof clarification per unit surface area occuring in the tank.

A sludge lift 80 transports the sludge accumulating at the lower end ofeach of the troughs 78 to a further trough 82 that is also inclinedtoward the center of the clarifier 10. The troughs 82 carry the sludgefrom the outlet of the lift 80 to the funnel 46 feeding the sludgeoutlet conduit 84 that extends vertically alongside the raw water inletpipe. The sludge lift can take a variety of forms, but a simple andpreferred form is a conduit with an associated pump. The lift gives thesludge additional height to be able to flow downhill to the center ofthe tank despite an inclined, downhill travel to reach the wall 50b. Italso allows the sludge to clear the water aeration and distributionfunctions occuring in the troughs 48 and 50. The lift 80 and theassociated troughs 82 are supported from the carriage with mounting armsnot shown for clarity.

Viewed broadly as a process, the present invention involves clarifyingwater by flotation simultaneously in multiple angular sectors of asingle, generally circular tank. This broad process is implemented bydistributing treated raw water to the tank along generally plural radiallines (corresponding to the lines of outlets on the headers 28) thatrotate through the tank. The process also involves simultaneouslyextracting clarified water from the tank from each sector, also alongplural, generally radial, rotating lines in the tank (corresponding tothe lines of inlets of the extractors 30). The distributing ispreferably with a net zero velocity. The distributing also preferablyincludes introducing dissolved air to the raw water at a central regionin the tank to produce the microscopic air bubbles in the raw water andthen distributing this treated, aerated water along the radial rotatinglines. The process of this invention also includes removing floatedsludge from the tank. This removal is also preferably along pluralrotating lines each associated with one of said distributing lines andone of said extracting lines.

In operation, the headers, extractors and scoops are preferably of likenumber and rotated about the center of the clarifier 10 in unison atabout 1/10 to 1/20 revolution per minute. With a forty-five meterdiameter tank having a depth of sixteen to eighteen inches, and with theheaders, extractors and scoops rotating at about 1/10 revolution perminute, and using three headers, three extractors and three scoops todefine three clarification sectors 64 within the tank, it is possible toclarify in the range of 100 to 130 liters per square meter, about fourto six times the rate possible with settling tanks of the same area.Looking at throughput capacity, this clarifier 10 utilizing the presentinvention can process eight to nine cubic meters of raw water persecond. This is twelve to thirteen times the throughput of the largestcommercially available SPC unit, namely, 0.73 m³ /sec., or 44.07 m³/min., or 11,800 gallons per minute for a seventy foot diameter tank.The clarifier 10 of this invention, with one unit having a 45m diameter,can clarify 184 m³ /min., or 265,000 m³ /day, or 70 million gallons perday. No known clarifier of any type can come close to this level ofperformance, and certainly not with this degree of compactness.

There has been described a water clarification apparatus and processwhich treats water at a higher throughput rate than has heretofore beenpossible using a comparable surface area for flotation removal of thesuspended solid contaminants. The unit is compact, has a comparativelysmall weight and a favorable cost of manufacture, particularly whencompared to collections of known sedimentation or even flotationclarifiers having the same treatment capacity. The apparatus of theinvention avoids hydraulic rotary seals at the inlets. It also has anautomatic water level control at the raw water feed. Further, theinvention can readily retrofit existing sedimentation tanks to increasetheir performance greatly with no increase in space utilization andusing existing feed lines.

While this invention has been described with respect to its preferredembodiments, it will be understood that various modifications andalterations will occur to those skilled in the art from the foregoingdetailed description and the accompanying drawings. For example, whilethe invention has been described with respect to flat, wide, box-likeheaders that receive treated water the header can have otherconfigurations, such as a circular or oval cross section, and theoutlets carried on the header can include the narrow gap to create themicroscopic bubbles directly in the tank, these arrangements, however,are viewed as similar but less efficient in the efficiency of theirdistribution and the reduction of turbulence in the tank. Similarly,water extraction can be accomplished using pipes or other conduits of avariety of shapes, and with the inlets at the bottom, upper or eventrailing surfaces. It is also possible to utilize a variety of otherarrangements to treat and distribute the raw water to the headers.Further, while the headers and extractors have been described asextending along substantially taught radial lines, they could be curvedwith respect to a radial line. These and other variations andmodifications are intended to fall within the scope of the appendedclaims.

What is claimed is:
 1. Apparatus for clarifying raw water using aflotation process where dissolved air is added to the raw water to formmicroscopic bubbles that attach to suspended particles to float them tothe surface of the raw water where they form a floating layer of sludge,the apparatus comprising a shallow tank with a circular outer wall and agenerally flat bottom wall, a raw water inlet at the center of the tank,a sludge removal pipe also located at the center of the tank, and aclarified water outlet,a plurality of mutually angularly spaced,radially extending header means that wherein each of said header meansdistributes the raw, aerated water with the microscopic bubbles thereinacross a radius of the tank, a corresponding plurality of extractormeans that are also mutually angularly spaced with respect to each otherand extend radially in the tank near its bottom wall for collectingclarified water near the bottom wall of said tank along the radiusthereof, means for rotating said plurality of header means andcorresponding extractor means around the tank continuously and in unisonwith each other, each said extractor means collecting water clarified inthe sector of the tank swept out by the rotation of the preceding headermeans, and means for continuously removing the sludge from the surfaceof the water in the tank and directing it to the sludge removal pipe. 2.The apparatus of claim 1 wherein said sludge removal means includes aplurality of rotatable scoops each associated with one of said headersand a corresponding one of said extractors, each of said scoops havingat least one blade extending radially over the tank and adapted to skimsludge from the surface of the water in said tank and to direct thescooped sludge to a passageway extending along said scoop, and furthercomprising carriage means for supporting and rotating said headers,extractors and scoops with said mutual angular spacing.
 3. The apparatusof claim 2 wherein said headers each have a set of mutually spacedoutlets arrayed along the header, dimensioned, and facing generallyopposite to the direction of rotation of the header itself to facilitatea generally uniform distribution of the raw, aerated water to the tankwith a net zero velocity relative to the tank.
 4. The apparatus of claim2 wherein there are n headers where n≧2, the headers, extractors andscoops are equiangularly spaced to divide the tank into n sectors andwherein the rate of rotation of said carriage means is coordinated withthe feed rate of the raw, aerated liquid to the tank to produce asubstantially complete clarification of the raw water in a given sectorin 1/n revolutions of the carriage.
 5. The apparatus of claim 1 furthercomprising means mounted within said tank around said raw water inletand said sludge collection pipe for aerating and distributing the raw,aerated water to said headers.
 6. The apparatus of claim 5 wherein saidaerating and distributing means includes (i) a first trough that rotatesin unison with said headers and said extractors, said trough having abottom wall, and outer side wall and an inner side wall, said firsttrough receiving a flow of the raw water from said raw water inlet, and(ii) an outlet manifold for a supply of pressurized water with airdissolved therein, that is disposed in the rotating trough to releasethe aerated water into the raw feed water to form the microscopicbubbles.
 7. The apparatus of claim 6 wherein said rotating first troughat least in part defines an annular clarified water collectioncompartment below said trough bottom wall, and wherein each of saidheaders is in fluid communication with the interior of said rotatingtrough to receive raw, aerated water therefrom and wherein each of saidextractors is in fluid communication with said clarified watercollection compartment which is open to said clarified water outlet. 8.The apparatus of claim 6 or 7 wherein said aerating and distributingmeans further includes a second trough having a bottom wall and an outerside wall, said second trough lying within said first rotating troughand adapted to receive the raw feed water from said inlet and feed itautomatically by overflow to said second trough.
 9. The apparatus ofclaim 8 wherein said second trough is stationary and its outer wall hasa downward facing flange that receives the outerwall of said firsttrough to facilitate said overflow feed from said second to said firsttroughs and to provide a sliding seal between said clarified watercollection compartment and the raw water in said first and secondtroughs.
 10. The apparatus of claim 8 wherein said first trough includesa spillover wall spaced radially outward from its inner wall to isolatethe turbulence of the spillover from the aeration at said outletmanifolds, and having a height less than that of the outer wall to setthe level of the water in said first trough and in the tank via saidheaders.
 11. The apparatus of claim 8 wherein said aerating anddistributing means further comprises a distribution ring for saidaerated water that is disposed in said second trough and is in fluidcommunication with said outlet manifolds in said first trough.
 12. Theapparatus of claim 2 wherein said sludge removal means further comprisesmeans for lifting the sludge collected from the surface of the waterheld in said tank to a level where it is fed by gravity to said sludgeremoval pipe.
 13. The apparatus of claim 12 wherein said sludge liftingmeans comprises a conduit and an associated pump.
 14. The apparatusaccording to claim 12 wherein said sludge lifting means comprisesforming said passageway so that it is associated with each blade of saidscoop and located radially offset from the axis of rotation of saidscoop whereby during one revolution of said scoop its blades each skimsaid sludge over one portion of the rotation, continued rotation directsit to the passageway, and further continued rotating performs said liftto a point where the sludge is dumped from the passageway.
 15. Theapparatus of claims 13 or 14 further comprising an inclined sludgetrough that receives the lifted sludge and directs it to said sludgeremoval pipe.
 16. The apparatus according to claim 6 wherein saidheaders are each formed as a box-like structure that is comparativelyflat, with an inlet open at an inner end wall to said first trough and aset of outlet open to the rear of said header as it rotates to producesaid net zero velocity distribution.
 17. The apparatus of claim 7wherein said extractors are each formed as a box-like structure that iscomparatively flat with an inlet located near the bottom of said tankand an outlet in fluid communication with said clarified watercollection compartment.
 18. The apparatus of claims 16 or 17 whereinsaid box-like structures increase in width as a function of radius topromote a uniform pressure distribution of the water moving therein.